A permanent magnet is generally used for a field system of an electric rotating apparatus from the viewpoint of a high efficiency. There is an axial gap type permanent magnet electric rotating apparatus in which a permanent magnet is arranged in a surface perpendicular to a shaft, an armature is arranged to oppose this permanent magnet, and an air gap is formed along the axial direction. A rotor of this electric rotating apparatus has an arrangement in which the permanent magnet is adhered to a rotor disk.
A plurality of rotors are arranged along the axial direction. The axial gap type permanent magnet electric rotating apparatus is configured such that armatures are arranged between the individual rotors, air gaps are formed between the rotors and armatures along the axial direction, and a magnetic flux passes from one rotor to another rotor on the opposite side through the armature.
When using this electric rotating apparatus as a generator, therefore, a magnetic flux generated from the permanent magnet by rotating the rotor by some power is passed, as a rotating magnetic field, through the armature. Thus, the armature can generate electric power.
As a related art, there is a double-rotor axial gap type permanent magnet electric rotating apparatus. This electric rotating apparatus has an arrangement in which permanent magnets embedded in back yokes of rotators are arranged in positions opposite to each other so as to sandwich an armature coil as a stator along the axial direction.
To obtain a high output when using a permanent magnet as a field system, it is necessary to use a high-performance magnet such as a neodymium magnet. Also, to make an electric rotating apparatus strong against demagnetization, it is necessary to use a neodymium magnet using a large amount of Dy (dysprosium). However, due to the scarcity of rare-earth materials, the cost of an electric rotating apparatus increases if a large amount of magnets are used.
Furthermore, the ratio of the processing cost of magnets is not low in the permanent magnet manufacturing cost. Therefore, the number of magnets has a large influence not only on the number of assembling steps as a whole but also on the magnet processing cost.
If, however, permanent magnets are arranged in a rotor so that different polarities are alternately arranged along the circumferential direction, permanent magnets equal in number to polarities are necessary, so the number of parts increases. In this case, it is necessary to use many permanent magnets requiring a complicated manufacturing process, high material cost, and high processing cost. This increases the overall cost of the electric rotating apparatus.